Science - USA (2022-02-04)

2550 cm–^1 at a spectral resolution of 1.25 cm–^1
( 16 ). Here, we report the results from an in-
dependent, physically based CrIS isoprene
retrieval scheme ( 17 ) that uses an optimal
estimation approach ( 16 ), which naturally

provides a full error characterization of the a

posteriori solution. We retrieve isoprene col-

umns from spectral features in the range 890

to 908 cm–^1 sampling 21 CrIS channels. The

retrieval scheme assumes the isoprene volume

mixing ratio to be height-invariant, so that the

geographical distribution of retrieved columns

is exclusively due to measurement informa-

tion, in contrast to ( 14 ). The vertical sensi-

tivity needed for quantitative interpretation

SCIENCEscience.org 4 FEBRUARY 2022•VOL 375 ISSUE 6580 563

A B C D E F

Fig. 2. GEOS-Chem model altitude-time cross sections of isoprene, NO, and some isoprene gas-phase and organic aerosol oxidation products over tropical
South America during April 2018.The region is defined as 6° to 12°S and 65° to 70°W and is denoted by the smaller rectangle in Fig. 1. (A) isoprene (ppbv).
(B) NO (ppbv). (C) Production rate of IEPOX (molec cm–^3 s–^1 ). (D) IEPOX (ppbv). (E) Production rate of IEPOX SOA (molec cm–^3 s–^1 ). (F) IEPOX-SOA (mgm–^3 at
standard conditions of 273 K and 1013 hPa unless otherwise stated). Time is expressed in days at Coordinated Universal Time (UTC). The solid black lines denote the
GEOS 3-hourly boundary layer height.

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